There is a growing demand for mounting of a liquid crystal panel for use in an electronic device such as a mobile phone or a digital camera with an optical sensor that has a sensing function of, in order to reduce power consumption and prevent a malfunction of a touch panel, controlling a display of the liquid crystal panel or invalidating a function of the touch panel by sensing a situation in which a user does not operate the electronic device, e.g., a case where a face comes close to the liquid crystal panel. Note here that a sensing function with respect to an object to be sensed of an optical sensor depends on an intensity of reflected light that is reflected from the object to be sensed and is incident on the optical sensor. This causes an output of the optical sensor to be inversely proportional to a distance between the object to be sensed and the optical sensor. There is also a demand for use of an optical sensor as a range sensor by use of such a characteristic as described above. Further, there has recently been a demand for use of an optical sensor as a gesture sensor by disposition of a plurality of photodiodes in the optical sensor to sense a movement of, for example, a hand from amounts of change in photocurrents that the photodiodes output in response to reflected light from objects to be sensed.
Note here that a liquid crystal panel for use in an electronic device such as a mobile phone or a digital camera mounted with such an optical sensor as described above is often used under illumination by an illuminating device provided outdoors or indoors. For this reason, even in a case where disturbance light is incident on the optical sensor, the liquid crystal panel is required to properly activate the optical sensor.
Such an optical sensor is exemplified by, for example, a light source direction sensor disclosed in Patent Literature 1. The light source direction sensor disclosed in Patent Literature 1 includes: a plurality of light-receiving elements; and a lens that collects optical signals from a light source into the light-receiving elements, the light source direction sensor causing an arithmetic processing section to carry out arithmetic processing with respect to a first optical signal detection value outputted by a first light-receiving element and a second optical signal detection value outputted by a second light-receiving element, and the light source direction sensor outputting a sensor output in accordance with values found by the arithmetic processing.
Next, there is a demand for disposition of a plurality of photodiodes in a light-receiving section of an optical sensor to sense a movement of an object from amounts of change in photocurrents that the photodiodes output in response to reflected light from objects to be sensed.
Such an optical sensor that senses a movement of an object is exemplified by, for example, a reflective sensor disclosed in Patent Literature 2. The reflective sensor disclosed in Patent Literature 2 includes: at least one light-emitting element; and a plurality of light-receiving elements for sensing light emitted by the at least one light-emitting element and reflected from an object to be sensed, the plurality of light-receiving elements being disposed at a distance from each other and collectively packaged with the at least one light-emitting element by a packaging member.
This reflective optical sensor, as shown in FIG. 20, includes a light-emitting element 301 and two light-receiving elements 302 and 303, with the light-receiving elements 302 and 303 disposed on both sides of the light-emitting element 301 respectively. In a case where an object to be sensed 304 is on the right side, light reflected from the object to be sensed 304 strongly strikes the light-receiving element 303. On the other hand, in a case where the object to be sensed 304 is on the left side, light reflected from the object to be sensed 304 strongly strikes the light-receiving element 302. Moreover, the position and/or movement of the object to be sensed 304 can be detected by reading a difference between a photocurrent generated in the light-receiving element 302 and a photocurrent generated in the light-receiving element 303.
Further, as a sensor that senses a movement of an object, there is also a demand for use of an optical sensor as a gesture sensor that senses a movement of, for example, a hand. Such a gesture sensor is used as an added function of a proximity sensor, and senses a movement of, for example, a hand over the touch panel in a noncontact manner. This makes it possible to operate a screen displayed on a liquid crystal panel, without contaminating a surface of the liquid crystal panel even with, for example, a wet hand or a dirty hand.
A conventional technique for allowing a sensor including a light-emitting element and a segmented photodiode to sense a direction of movement of an object to be sensed is exemplified by, for example, a technique disclosed in Patent Literature 3. Patent Literature 3 discloses a configuration in which multilayer metal is stacked on a light-emitting element and a four segmented photodiode (light-receiving elements). These light-receiving elements each have directivity (sensitivity) in a corresponding one of an upward direction, a downward direction, a rightward direction, and a leftward direction. According to Patent Literature 3, a direction of movement of an object to be sensed is sensed by obtaining (i) a difference between a signal from the light-receiving element having directivity in the upward direction and a signal from the light-receiving element having directivity in the downward direction and (i) a difference between a signal from the light-receiving element having directivity in the leftward direction and a signal from the light-receiving element having directivity in the rightward direction.
Such an electronic device mounted with an optical sensor is used outdoors or indoors. For this reason, even in a case where disturbance light attributed to natural light or illuminating light is incident on the optical sensor, the electronic device is required to properly activate the optical sensor. In particular, a gesture sensor that detects a movement of an object to be sensed is supposed to be used under intense disturbance light such as natural light or illuminating light. This further requires the gesture sensor to be properly activated in a case where disturbance light attributed to natural light or illuminating light is incident on the optical sensor.